Improving frictional properties in lubricant composition has been an objective of the industry. Friction between two surfaces will increase the power required to effect movement and where the movement is an integral part of an energy conversion system, it is most desirable to effect lubrication in a manner which will minimize this friction. By minimizing friction in a lubricant system, fuel economy and energy efficiency are maximized. Friction modifiers have been used to promote such friction-reducing properties in lubricant systems.
Friction modifiers are well-known in the art and are currently used in engine oil formulations. Friction modifiers know in the art include glycerol mono-, di- and tri-oleate and mixtures thereof, oleylamide, ethoxylated amines such as Duomeen® TDO, alkyl dithiocarbamates, molybdenum dialkyldithiocarbamates, trinuclear organomolybdenum compounds.
Friction modifiers are not commonly known to improve the viscosity index (VI) of a lubricant. Generally, VI improvers are olefin polymers such as polyisobutylene, ethylene propylene copolymers, hydrogenated polymers and copolymers and terpolymers of styrene with isoprene and/or butadiene, polymers of alkyl acrylates or alkyl methacrylates, copolymers of alkylmethacrylates with N-vinylpyrrolidone or dimethylaminoalkyl methacrylate, post grafted polymers of ethylene-propylene with an active monomer such as maleic anhydride which may be further reacted with an alcohol or an alkylene polyamine, styrene-maleic anhydride polymers post reacted with alcohols and amines and the like. These materials function by increasing the viscosity of the base oil proportionately more at high temperatures than at low temperatures. VI improvers are a well-known separate class of additives than the friction modifiers. Most, if not all engine lubricant compositions, are formulated with both VI improvers and friction modifiers.
In the prior art, many friction modifier additives have been suggested and used. For example, U.S. Pat. No. 4,839,068 is directed to polyesters in lubricant compositions that act as friction reducers, viscosity improvers and film-forming enhancers. The lubricant composition comprises mineral oil and at least one polysuccinate ester wherein the succinate group contain alkyl or alkenyl substituents.
U.S. Pat. No. 4,683,069 relates to lubricant oil compositions exhibiting improved fuel economy which contain 0.05 to 0.2 wt % of a glycerol partial ester of a C16-C18 fatty acid as the fuel economy additive.
U.S. Pat. No. 4,707,301 is directed to lubricant additives that improve friction modifying properties in functional fluids. The lubricant additives comprise dimer ester and polyester materials derived from adducts of O, O-dialkyl dithiophosphoric acids and 5-norbornene-2,3-dicarboxylic anhydride.
EP 0259808 is directed to lubricating oil compositions exhibiting good frictional characteristics, where the composition comprises a mineral oil and polyester, which includes hindered esters and dicarboxylic acid esters.
EP 0815186 is directed to polyolester compositions, which exhibit lower friction coefficient when compared to conventional synthetic esters, having unconverted hydroxyl groups.
Despite the advances in lubricant oil formulation technology, there remains a need for an additive that will effectively reduce the friction coefficient of oil based lubricants and additionally improve VI and solvency in said lubricants.